It’s 2013, and the web is no longer made up of “web pages.” It’s full of web applications. They are morally equivalent to your desktop applications, and they should be treated as such. That means Gmail shouldn’t be hidden amongst the million other tabs and browser windows you have open; it should be in its own dedicated window.
To this end, Chrome provides this feature called “application shortcuts.” Basically, it lets you create desktop shortcuts that launch Chrome with a single URL, say “http://www.gmail.com/”, in a dedicated window without any UI (or “chrome”). Similarly, people pay $4.99 for Fluid, an OS X application which does much the same thing.
It’s barely worth calling a “feature” because the one trivial thing it does is hide the URL bar and the tab bar. Yet it’s an essential feature. The cost:benefit ratio of implementing it is sky-high.
Back in 2007, the distant past, Mozilla had the Prism project, which aimed to implement exactly this. Well, the project died; I don’t know why. It was then taken up by the Chromeless project. Well, what do you know, that project died, too. At the same time, Prism was taken up by an independent company, who called it WebRunner. Guess what happened to it? It’s dead. Six years and three entire “projects” later, and still no-one has worked out how to remove that one centimeter of UI from the top of the Firefox window.
It’s sad and strange. Mozilla have created some amazing things, yet basic features are completely missing.
Update: it’s 2015, the web has even more applications, and there is no hint of an application-specific browser from Mozilla. Let’s speak again in 2017 …